1. Field of the Invention
The present invention relates to a double-layer vacuum container including a vacuum space between an inner container and an outer container which constitute a metal double-layer container.
2. Description of the Related Art
Such a double-layer vacuum container is widely used in the following manner. The double-layer vacuum container stores various types of beverage such as green tea, coffee, black tea or an isotonic drink therein so as to keep the beverage warm or cold. The double-layer vacuum container also serves to pour a drink by means of a motor pump, a manual pump or inclination, to directly serve a drink through a spout, to serve a drink through a straw or the like in accordance with each use and intended purpose.
With reference to FIG. 1 illustrating an embodiment of the present invention, the double-layer vacuum container is constituted by a metal inner container 1 and a metal outer container 2. A lip 1a of the inner container 1 and a lip 2a of the outer container 2 are welded to each other so as to be integrally formed. Then, an exhaust port provided in a portion of the outer container 2 is sealed after the container is pumped to a vacuum through the exhaust port, thereby obtaining a vacuum space 3 between the inner container 1 and the outer container 2.
However, since the lip 1a is supported merely through bonding to the lip 2a of the outer container 2a although the inner container 1 stores a liquid to have significantly increased weight, the inner container 1 is likely to be affected by a shake or vibration. For example, an inertia force may be applied by rough handling of the container, shaking when the container is carried or the like, a sudden change in movement, a fall or the like, which may displace or damage the container. In particular, in accordance with the requirements of streamlining the shape of the double-layer vacuum container, a gap between the inner container 1 and the outer container 2 is set to an extremely small value. As a result, however, the inner container 1 and the outer container 2 are brought into contact with each other by the displacement to be likely to degrade its heat retaining property.
In order to overcome such a problem, a metal double-layer vacuum container, in which an inner container and an outer container are brought into point contact or line contact at a plurality of positions in a circumferential direction under the middle of their body portions, is known (for example, see Japanese Utility Model Laid-Open Publication No. Hei 7-27430). In this structure, in addition to a bonded portion at the lip between the inner container and the outer container, a part of the inner container under the middle of the body portion is also supported by the contact portions with the outer container at a plurality of positions in a circumferential direction. Therefore, shakes or displacement of the inner container can be prevented. Moreover, the degradation of a heat retaining property due to heat conduction from the inner container to the outer container can be restrained to a certain degree because the contact between the inner container and the outer container is achieved by point contact or line contact at a plurality of positions.
In the above-described conventional example, however, the supporting portion of the outer container under the middle of the body portion of the inner container directly conducts heat to an externally exposed portion of the outer container or has a short thermal conduction path to the externally exposed portion of the outer container. Therefore, a sufficient heat retaining property has not been obtained.